Monitoring of shaft doors is used in order to help ensure the safety of persons present in the elevator installation.
An elevator installation usually comprises an elevator shaft with a plurality of shaft doors and an elevator cage movable in the elevator shaft. Each shaft door is secured by a locking device. A shaft door contact is arranged at the locking device for the purpose of detection of unlocking. The shaft door contacts of several shaft doors are connected in series in a closed current circuit and are a component of a safety circuit. The closed current circuit is acted on by a basic voltage. In the case of unlocking of one of the shaft doors not attributable to a usual user-related utilization of the elevator cage this safety circuit is interrupted by the associated shaft door contact. After such an unlocking the assumption can be that a person is present in the elevator shaft outside the elevator cage. This can be caused by, for example, manual unlocking of the shaft door, but also by faulty functioning of the locking device.
Independently of re-locking subsequently taking place, an operating mode of the elevator installation is adapted. Travel or speed limitations are incorporated into a travel pattern of the elevator cage. It can thus be ensured that a person possibly present on the elevator cage or on the floor of the elevator shaft has sufficient room. The elevator installation can, instead, also be stopped as a precaution. In both cases a service specialist thereafter has to ensure on site that nobody is present in the elevator shaft outside the elevator cage. Only then can the specialist reset the elevator installation back to an operating mode corresponding with normal operation.
It can be problematic with such a procedure that the device for monitoring the shaft doors is ‘blind’ in the case of a longer-term power failure in which the basic voltage in the safety circuit cannot be maintained by a battery. Consequently, for reasons of safety it should be assumed after a longer-term power failure that a person is present in the shaft, although it is also possible that none of the shaft doors was unlocked during the power failure. It can thus be necessary in every instance for a service specialist to be on site if the power supply is guaranteed again and the elevator installation can be set back into normal operation.